U.S. patent number 5,624,234 [Application Number 08/471,270] was granted by the patent office on 1997-04-29 for fan blade with curved planform and high-lift airfoil having bulbous leading edge.
This patent grant is currently assigned to ITT Automotive Electrical Systems, Inc.. Invention is credited to Michael J. Neely, John R. Savage.
United States Patent |
5,624,234 |
Neely , et al. |
April 29, 1997 |
Fan blade with curved planform and high-lift airfoil having bulbous
leading edge
Abstract
A blade for a vehicle engine-cooling fan assembly having a
curved planform and a high-lift airfoil. The planform has a first
region adjacent the root of the blade with forward curvature, a
second region adjacent the tip of the blade with backward
curvature, and an intermediate region disposed between the first
region and the second region with substantially straight curvature.
The airfoil has a leading edge; a rounded, bulbous nose section
adjacent the leading edge; a trailing edge; a curved pressure
surface extending smoothly and without discontinuity from the nose
section to the trailing edge; a curved suction surface extending
smoothly and without discontinuity from the nose section to the
trailing edge; and a thin, highly cambered aft section formed
adjacent the trailing edge and between the pressure surface and the
suction surface. The nose section has a thickness which is greater
than the thickness of the airfoil between the pressure surface and
the suction surface and the nose section blends smoothly into the
pressure surface and the suction surface.
Inventors: |
Neely; Michael J. (Dayton,
OH), Savage; John R. (Kettering, OH) |
Assignee: |
ITT Automotive Electrical Systems,
Inc. (Auburn Hills, MI)
|
Family
ID: |
26992971 |
Appl.
No.: |
08/471,270 |
Filed: |
June 6, 1995 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
342358 |
Nov 18, 1994 |
|
|
|
|
Current U.S.
Class: |
416/238; 416/189;
416/242 |
Current CPC
Class: |
F04D
29/326 (20130101); F04D 29/384 (20130101) |
Current International
Class: |
F04D
29/38 (20060101); F04D 29/32 (20060101); F04D
029/38 () |
Field of
Search: |
;416/238,189R,169A,242 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0482788 |
|
Apr 1992 |
|
EP |
|
410800 |
|
Sep 1923 |
|
DE |
|
3640780 |
|
Oct 1988 |
|
DE |
|
4326147 |
|
Nov 1994 |
|
DE |
|
Other References
International Search Report dated Apr. 25, 1996..
|
Primary Examiner: Look; Edward K.
Assistant Examiner: Sgantzos; Mark
Attorney, Agent or Firm: Twomey; Thomas N. Lewis; J.
Gordon
Parent Case Text
This is a continuation-in-part of U.S. patent application Ser. No.
08/342,358 filed on Nov. 18, 1994.
Claims
What is claimed is:
1. A planform defining the shape of blades of a vehicle
engine-cooling fan assembly, each blade having a root, a tip, and a
span between the root and tip, said planform comprising:
a first region adjacent the root of the blade having forward
curvature;
a second region adjacent the tip of the blade having backward
curvature; and
an intermediate region disposed between said first region and said
second region having substantially straight curvature.
2. The planform according to claim 1 wherein said first region
having forward curvature extends from the root to a terminus
located about forty-percent of the span of the blade.
3. The planform according to claim 2 wherein said intermediate
region having substantially straight curvature extends from said
terminus of said first region to an end point located about
sixty-percent of the span of the blade and said second region
having backward curvature extends from said end point of said
intermediate region to the tip of the blade.
4. The planform according to claim 1 wherein said second region
having backward curvature extends from the tip to an end point of
said intermediate region located between about sixty and
seventy-percent of the span of the blade.
5. A vehicle fan assembly for circulating air to cool an engine,
said fan assembly comprising:
a central hub; and
a plurality of blades with a planform, a root joined to said hub, a
tip, and a span between said root and said tip, said blades
extending generally radially outward from said hub and each said
planform having:
(a) a first region adjacent said root of said blade with forward
curvature;
(b) a second region adjacent said tip of said blade with backward
curvature; and p2 (c) an intermediate region disposed between said
first region and said second region with substantially straight
curvature.
6. The vehicle fan assembly according to claim 5 further comprising
an outer ring, said blades extending generally radially outward
from said hub to said ring.
7. The vehicle fan assembly according to claim 6 wherein said ring
has an axial depth of about 23 mm.
8. The vehicle fan assembly according to claim 5 wherein said first
region with forward curvature extends from said root to a terminus
located about forty-percent of said span of said blade.
9. The vehicle fan assembly according to claim 8 wherein said
intermediate region with substantially straight curvature extends
from said terminus of said first region to an end point located
about sixty-percent of said span of said blade and said second
region with backward curvature extends from said end point of said
intermediate region to said tip of said blade.
10. The vehicle fan assembly according to claim 5 wherein said
second region with backward curvature extends from said tip to an
end point of said intermediate region located between about sixty
and seventy-percent of said span of said blade.
11. A blade for a vehicle engine-cooling fan assembly
comprising:
a root;
a tip;
a span between said root and said tip;
a planform having:
(a) a first region adjacent said root of said blade with forward
curvature.
(b) a second region adjacent said tip of said blade with backward
curvature, and
(c) an intermediate region disposed between said first region and
said second region with substantially straight curvature; and
an airfoil section having:
(a) a leading edge,
(b) a rounded, bulbous nose section adjacent said leading edge,
(c) a trailing edge,
(d) a curved pressure surface extending smoothly and without
discontinuity from said nose section to said trailing edge,
(e) a curved suction surface extending smoothly and without
discontinuity from said nose section to said trailing edge, and
(f) a thin, highly cambered aft section formed adjacent said
trailing edge and between said pressure surface and said suction
surface, said aft section having a location of maximum camber,
said nose section having a thickness which is greater than the
thickness of said airfoil section between said pressure surface and
said suction surface and said nose section blending smoothly into
said pressure surface and said suction surface.
12. The blade according to claim 11 wherein said first region with
forward curvature extends from said root to a terminus located
about forty-percent of said span of said blade.
13. The blade according to claim 12 wherein said intermediate
region with substantially straight curvature extends from said
terminus of said first region to an end point located about
sixty-percent of said span of said blade and said second region
with backward curvature extends from said end point of said
intermediate region to said tip of said blade.
14. The blade according to claim 11 wherein said second region with
backward curvature extends from said tip to an end point of said
intermediate region located between about sixty and seventy-percent
of said span of said blade.
15. A vehicle fan assembly for circulating air to cool an engine,
said fan assembly comprising:
a central hub; and
a plurality of blades, each blade having:
(a) a root,
(b) a tip,
(c) a span between said root and said tip,
(d) a planform including:
(1) a first region adjacent said root of said blade with forward
curvature:
(2) a second region adjacent said tip of said blade with backward
curvature; and
(3) an intermediate region disposed between said first region and
said second region with substantially straight curvature, and
(e) an airfoil section including:
(1) a leading edge;
(2) a rounded, bulbous nose section adjacent said leading edge;
(3) a trailing edge;
(4) a curved pressure surface extending smoothly and without
discontinuity from said nose section to said trailing edge;
(5) a curved suction surface extending smoothly and without
discontinuity from said nose section to said trailing edge; and
(6) a thin, highly cambered aft section formed adjacent said
trailing edge and between said pressure surface and said suction
surface, said aft section having a location of maximum camber,
said nose section having a thickness which is greater than the
thickness of said airfoil section between said pressure surface and
said suction surface and said nose section blending smoothly into
said pressure surface and said suction surface.
16. The vehicle fan assembly according to claim 15 further
comprising an outer ring, said blades extending generally radially
outward from said hub to said ring.
17. The vehicle fan assembly according to claim 16 wherein said
ring has an axial depth of about 23 mm.
18. The vehicle fan assembly according to claim 15 wherein said
first region with forward curvature extends from said root to a
terminus located about forty-percent of said span of said
blade.
19. The vehicle fan assembly according to claim 18 wherein said
intermediate region with substantially straight curvature extends
from said terminus of said first region to all end point located
about sixty-percent of said span of said blade and said second
region with backward curvature extends from said end point of said
intermediate region to said tip of said blade.
20. The vehicle fan assembly according to claim 15 wherein said
second region with backward curvature extends from said tip to an
end point of said intermediate region located between about sixty
and seventy-percent of said span of said blade.
Description
FIELD OF THE INVENTION
This invention relates generally to a vehicle engine-cooling fan
assembly and, more particularly, to the fan blade of such an
assembly. The fan blade combines a curved planform with a high-lift
airfoil having a bulbous nose adjacent its leading edge which
smoothly merges into both the pressure and suction surfaces of the
airfoil.
BACKGROUND OF THE INVENTION
A multi-bladed cooling air fan assembly 10 (which incorporates the
present invention) is shown in FIG. 1. Designed for use in a land
vehicle, fan assembly 10 induces air flow through a radiator to
cool the engine. Fan assembly 10 has a hub 12 and an outer,
rotating ring 14 that prevents the passage of recirculating flow
from the outlet to the inlet side of the fan. A plurality of blades
100 (seven are shown in FIG. 1) extend radially from hub 12 (where
the root of each blade 100 is joined) to ring 14 (where the tip of
each blade 100 is joined).
Fan assembly 10 must accommodate a number of diverse
considerations. For example, when fan assembly 10 is used in an
automobile, it is placed behind the radiator. Consequently, fan
assembly 10 must be compact to meet space limitations in the engine
compartment. Fan assembly 10 must also be efficient, avoiding
wasted energy which directs air in turbulent flow patterns away
from the desired axial flow; relatively quiet; and strong to
withstand the considerable loads generated by air flows and
centrifugal forces.
Generally, blades 100 are "unskewed." Such blades have a straight
planform in which a radial center line of blade 100 is straight and
the blade chords perpendicular to that line are uniformly
distributed about the line. Occasionally, blades 100 are forwardly
skewed: the blade center line curves in the direction of rotation
of fan assembly 10 as the blade extends radially from hub 12 to
ring 14. U.S. Pat. No. 4,358,245, assigned to Airflow Research and
Manufacturing Corporation (ARMC), discloses a forwardly skewed fan
blade in which the blade angle increases over the outer 30% of the
blade.
U.S. Pat. No. 5,393,199 also discloses a fan blade forwardly skewed
at least along the portion of the blade adjacent the tip (see
column 5, line 55 through column 6, line 44). Each blade has
leading and trailing edges which include a portion adjacent the
root substantially collinear with the respective radius extending
from the center of the fan. In FIG. 8 of the '199 patent, the
collinear portions are represented by X1, X2, and X3.
Other blades 100 are backwardly (away from the direction of fan
rotation) skewed. General Motors Corporation has used a fan blade
with a modest backward skew on its "X-Car." The blade angle of that
fan blade increases with increasing diameter along the outer
portion of the blades and the skew angle at the blade tip is about
40.degree. . U.S. Pat. No. 4,569,632, assigned to ARMC, discloses
an axial flow fan with blades that are increasingly backward-skewed
as a function of movement from hub to ring. The blades are oriented
at a pitch ratio which continuously decreases as a function of
increasing blade radius along the radially outermost 30% of the
blade.
Still other blades 100 are backwardly skewed in the root region of
the blade adjacent the hub of fan assembly 10 and forwardly skewed
in the tip region of the blade. U.S. Pat. No. 4,569,631 (also
assigned to ARMC); No. 4,684,324; and No. 5,064,345 each disclose
such a blade. Each of these references teach a short, abrupt
transition region (if any) between the root region of backward skew
and the tip region of forward skew. For example, the '345 patent
specifically discloses a transition region of no greater than 0.01
R, where R is the fan radius.
To improve the operation of fan assembly 10, much attention has
focused on the design or shape of the blade airfoils. High lift and
efficiency are required to meet the ever-increasing operational
standards for vehicle engine-cooling fan assemblies. There are many
different airfoil shapes and slight variations in shape alter the
characteristics of the airfoil in one way or another.
Because only slight variations in airfoil design yield large
differences in aerodynamic performance, a multitude of different
airfoils were developed by approximately 1920. At that time, there
was no orderly system of identifying the different airfoils. Those
that seemed to prove effective were simply given arbitrary
designations such as RAF 6, Gottingen G-398, and Clark Y.
The National Advisory Committee for Aeronautics (NACA), which was
the forerunner of NASA, developed an identification system in the
late 1920s. NACA's wind tunnel tests showed that the aerodynamic
characteristics of airfoils depend primarily upon two shape
variables: the thickness form and the mean-line form. NACA then
proceeded to identify these characteristics in a numbering system
for the airfoils.
The first such airfoils are referred to by the NACA four-digit
series. The NACA 2412 airfoil is a typical example. The first
number (2 in this case) is the maximum camber in percent (or
hundredths) of chord length. The second number, 4, represents the
location of the maximum camber point in tenths of chord and the
last two numbers, 12, identify the maximum thickness in percent of
chord. All characteristics are based on chord length (c) because
they are all proportional to the chord. For this airfoil, the
maximum camber is 0.02 c, the location of maximum camber is 0.4 c,
and the maximum thickness is 0.12 c.
The flat plate 20, shown in FIG. 2a in an air stream 18, is the
simplest of airfoils. At zero angle of attack (.alpha.), flat plate
20 produces no lift because it is actually a symmetrical airfoil
(it has no camber). At a slightly positive angle of attack,
however, flat plate 20 will produce lift, as shown in FIG. 2b. Flat
plate 20 is not a very efficient airfoil because it creates a fair
amount of drag. The sharp leading edge 22 also promotes stall at a
very small angle of attack and, therefore, severely limits the
lift-producing ability of flat plate 20. The stall condition is
illustrated in FIG. 2c.
For these reasons, airfoils were provided with a curved nose
adjacent the leading edge. That modification enables the airfoil to
achieve higher angles of attack without stalling. Such an airfoil
is efficient, however, only over a small range of angles.
Accordingly, the curved nose was filled in so that a wider range of
angles of attack was possible. These thicker airfoils displayed
greater lifting capability and finally evolved into the shape shown
in FIGS. 3a and 3b, recognized as the "typical" or "classic"
thicker airfoil 30.
FIG. 3a illustrates the conventional thicker airfoil 30 having a
leading edge 32, a trailing edge 34, and substantially parallel
surfaces 36 and 38. The chord of thicker airfoil 30 is the straight
line (represented by the dimension "c") extending directly across
the airfoil from leading edge 32 to trailing edge 34. The camber is
the arching curve (represented by the dimension "a") extending
along the center or mean line 40 of thicker airfoil 30 from leading
edge 32 to trailing edge 34. Camber is measured from a line
extending between the leading and trailing edges of the airfoil
(i.e., the chord length) and mean line 40 of thicker airfoil
30.
As shown in FIG. 3b, when thicker airfoil 30 contacts a stream of
air 18, the air stream engages leading edge 32 and separates into
streams 42 and 44. Stream 42 passes along surface 36 while stream
44 passes along surface 38. As is well known, stream 42 travels a
greater distance than stream 44, at a higher velocity, with the
result that air adjacent to surface 36 is at a lower pressure than
air adjacent to surface 38. Consequently, surface 36 is called the
"suction side" of thicker airfoil 30 and surface 38 is called the
"pressure side" of thicker airfoil 30. The pressure differential
creates lift.
Airfoils with the classic profile of thicker airfoil 30 illustrated
in FIGS. 3a and 3b have been used in engine-cooling fan assemblies.
Such airfoils improved fan efficiency relative to contemporary,
competing airfoil profiles. They have been unable, however, to
provide the higher lift-to-drag ratios now desired for automotive
applications. High lift and increased efficiency are needed to meet
higher operational standards for vehicle engine-cooling fan
assemblies. Accordingly, additional airfoil designs have been
developed.
U.S. Pat. No. 5,151,014, assigned to ARMC, discloses an airfoil
having a reduced, substantially constant thickness over most of its
chord length. Accordingly, the ARMC airfoil 50 (see FIGS. 4a, 4b,
and 4c which correspond to FIGS. 2a, 2b, and 3, respectively, in
the '014 patent) is lighter than thicker airfoil 30 and,
ostensibly, offers increased efficiency. ARMC airfoil 50 has a
leading edge 52, a trailing edge 54, and substantially parallel
suction surface 56 and pressure surface 58.
Pressure surface 58 has a first sharp corner 60, such that pressure
surface 58 diverges or bends towards suction surface 56, thereby
creating a thick nose section 62 and a reduced thickness portion
64. The distance between corner 60 and leading edge 52 is between
5% and 10% of the chord length of ARMC airfoil 50. Pressure surface
58 also has a second sharp corner 61 upon termination of straight
line portion 59 of pressure surface 58. The dashed line 66 in FIGS.
4a and 4b illustrates the pressure surface of thicker airfoil
30.
FIG. 4b illustrates the flow of air over ARMC airfoil 50. A stream
of air 18 intersects ARMC airfoil 50 at leading edge 52 and
separates into streams 68 and 70. Stream 68 flows along suction
surface 56. Stream 70 may not flow, however, along pressure surface
58. According to the '014 patent, stream 70 will separate from
pressure surface 58 at corner 60 and will follow a path similar to
the path followed by stream 44 for thicker airfoil 30 shown in FIG.
3b. Therefore, ARMC airfoil 50 appears to have substantially the
same flow characteristics as thicker airfoil 30.
To assure that stream 70 separates from pressure surface 58, the
angle at which pressure surface 58 diverges at corner 60 must be
greater than a threshold angle. If the bend is too gradual, stream
70 will turn at corner 60 and remain close to pressure surface
58--resulting in increased loading and noise. Referring to FIG. 4c,
corner 60 bends at an angle .theta. of at least 30.degree.. Angle
.theta. is measured between lines tangent to pressure surface 58 on
each side of corner 60. Although the air flow disclosed in the '014
patent may occur, it is unnecessary for the design of a high-lift,
lightweight airfoil.
U.S. Pat. No. 4,692,098, assigned initially to General Motors
Corporation, discloses an airfoil shaped for improved pressure
recovery. In this design, a discontinuity in the form of a flat,
step, scribe mark, cavity, or surface roughness is made on the
suction surface 86--rather than on the pressure surface 88--of the
discontinuous airfoil 80 of the '098 patent (see FIG. 5 which
corresponds to FIG. 4 in the '098 patent). Preferably, a flat 82
transverse to the chord of discontinuous airfoil 80 and adjacent to
the airfoil nose 84 is provided on suction surface 86. Flat 82
extends rearward from a sharp edge 94 that is located toward the
forward end of the laminar boundary layer region. Flat 82 forms a
ramp that makes a 9.degree. angle with a tangent line 96 to the
upstream suction surface 86 of discontinuous airfoil 80.
Discontinuous airfoil 80 also has a rounded leading edge 90, a
trailing edge 92, and a so-called Stratford recovery region that
connects flat 82 to trailing edge 92.
Discontinuous airfoil 80 is designed to control the size and
location of the laminar separation bubble that forms on suction
surface 86 as the airfoil operates in a low-Reynolds-number
environment. Airfoils of this type are very effective at reducing
the size of the laminar separation bubble and ensuring the
re-attachment of flow on suction surface 86. By controlling the
separation and re-attachment in this manner, discontinuous airfoil
80 operates at a high lift-to-drag ratio.
Airfoils like discontinuous airfoil 80 have been used for many
years in engine-cooling fan assemblies on General Motors vehicles.
On an airfoil with a straight planform, a discontinuous airfoil 80
with a flat 82 provides excellent performance across a wide
operating range. On the new, backward-curved blades used (for
example) in the air conditioning systems without chlorinated
fluorocarbons (CFCs), however, discontinuous airfoil 80 is not as
effective as an airfoil with a smooth, continuous suction
surface.
To overcome the shortcomings of conventional fan assemblies, a new
fan assembly is provided. An object of the present invention is to
provide an engine-cooling fan assembly, including a plurality of
blades, having operational and air-pumping efficiency. Another
object is to provide an improved fan assembly having a compact
configuration. Still another object of the present invention is to
reduce the noise created by the fan assembly. It is still another
object of the present invention to reduce the axial depth of the
ring of the fan assembly.
Blades produce turning of the air stream through the fan assembly,
thereby creating a pressure rise across the assembly. Yet another
object of the present invention is to provide a fan assembly in
which the fan blades combine a curved planform with a high-lift
airfoil. The airfoil of the fan blades has a bulbous nose adjacent
its leading edge which smoothly merges into both the pressure and
suction surfaces of the airfoil. A related object is to provide a
blade in an engine-cooling fan assembly that provides high pressure
rise across the fan assembly and reduced mass. Finally, it is an
object of the present invention to provide a blade design suitable
for the entire range of engine-cooling fan assembly operation,
including idle.
SUMMARY OF THE INVENTION
To achieve these and other objects, and in view of its purposes,
the present invention provides a blade (for a vehicle
engine-cooling fan assembly) having a curved planform and a
high-lift airfoil. The planform has a first region adjacent the
root of the blade with forward curvature, a second region adjacent
the tip of the blade with backward curvature, and an intermediate
region disposed between the first region and the second region with
substantially straight curvature. The airfoil has a leading edge; a
rounded, bulbous nose section adjacent the leading edge; a trailing
edge; a curved pressure surface extending smoothly and without
discontinuity from the nose section to the trailing edge; a curved
suction surface extending smoothly and without discontinuity from
the nose section to the trailing edge; and a thin, highly cambered
aft section formed adjacent the trailing edge and between the
pressure surface and the suction surface. The nose section has a
thickness which is greater than the thickness of the airfoil
between the pressure surface and the suction surface and the nose
section blends smoothly into the pressure surface and the suction
surface.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary, but are not
restrictive, of the invention.
BRIEF DESCRIPTION OF THE DRAWING
The invention is best understood from the following detailed
description when read in connection with the accompanying drawing,
in which:
FIG. 1 is a front elevational view of a multibladed cooling air fan
assembly incorporating blades having the airfoil and planform of
the present invention;
FIG. 2a illustrates a conventional flat plate airfoil in an
airstream;
FIG. 2b is the flat plate airfoil illustrated in FIG. 2a showing
the airstream at a slight angle of attack;
FIG. 2c is the flat plate airfoil illustrated in FIG. 2a during a
stalled condition;
FIG. 3a is a cross-sectional view of a conventional thicker
airfoil;
FIG. 3b illustrates the conventional thicker airfoil, shown in FIG.
3a, in an airstream;
FIG. 4a is a cross-sectional view of a prior art ARMC airfoil;
FIG. 4b illustrates the ARMC airfoil, shown in FIG. 4a, in an
airstream;
FIG. 4c is an enlarged view of a section of the ARMC airfoil shown
in FIG. 4a;
FIG. 5 is a cross-sectional view of a conventional discontinuous
airfoil;
FIG. 6 is a cross-sectional view of the airfoil of the blade of the
present invention;
FIG. 7 is a comparison between the thicker airfoil shown in FIG. 3a
and the airfoil of the blade of the present invention shown in FIG.
6;
FIG. 8 is a graph of Coefficient of Lift (C.sub.L) versus Angle of
Attack (.alpha.) for an airfoil with higher and lower camber;
FIG. 9a shows the axial depth of the ring of the fan assembly of
FIG. 1 when the airfoil has a high angle of attack;
FIG. 9b shows the axial depth of the ring of the fan assembly of
FIG. 1 when the airfoil has a low angle of attack;
FIG. 10 is a graph of fan assembly static efficiency versus fan
assembly operating point, comparing the airfoil of the blade of the
present invention, shown in FIG. 6, with the conventional thicker
airfoil, shown in FIG. 3a;
FIG. 11 is an overlay of the prior art ARMC airfoil, shown in FIG.
4a, on the airfoil of the blade of the present invention, shown in
FIG. 6;
FIG. 12 is an enlarged view of a section of the airfoil of the
blade of the present invention shown in FIG. 6;
FIG. 13 illustrates a blade with a conventional, straight
planform;
FIG. 14a illustrates a blade with a highly-curved blade
planform;
FIG. 14b shows the streamlines of the complex, three-dimensional
flowfield over the highly-curved blade planform illustrated in FIG.
14a;
FIG. 15 illustrates the skew angle for measuring the magnitude of
the planform curvature of the blade of the present invention;
FIG. 16 shows the blade having a planform with regions of forward,
straight, and backward curvature according to the present
invention;
FIG. 17 is a graph of normalized total pressure versus span ratio
for blades with forward, straight, and backward curvature;
FIG. 18a illustrates a typical inlet velocity diagram for an
airfoil of a blade with a straight planform;
FIG. 18b illustrates a typical inlet velocity diagram for an
airfoil of a blade with a curved planform; and
FIG. 19 shows the pressure surface of the blade--combining the
high-lift airfoil having a bulbous leading edge shown in FIG. 6
with the 40% forward curvature, 20% straight, 40% backward
curvature planform from hub to ring shown in FIG. 16--according to
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawing, FIG. 6 shows the airfoil of blade 100
according to the present invention. Blade 100 is used in an
engine-cooling fan blade assembly 10 (see FIG. 1). It is emphasized
that, according to common practice, the various features of the
drawing are not to scale. On the contrary, the width or length and
thickness of the various features are arbitrarily expanded or
reduced for clarity.
The airfoil of blade 100 has a suction surface 102 and a pressure
surface 104 which meet at the leading edge 106 and the trailing
edge 108. A rounded, thick, bulbous nose section 110 merges
smoothly with the thin, highly-cambered aft section 112 on both
suction surface 102 and pressure surface 104. There are no
discontinuities or abrupt changes on either suction surface 102 or
pressure surface 104.
The airfoil of blade 100 presents an angle of attack (.alpha.) with
air stream 18. Rounded, thick, bulbous nose section 110 prevents
separation as the air traverses the airfoil of blade 100 from
leading edge 106 to trailing edge 108. The camber of the airfoil of
blade 100 is the arching curve (represented by the dimension "b")
extending along the center or mean line 114 from leading edge 106
to trailing edge 108. Thin aft section 112 provides high camber
and, consequently, high lift. The camber at the location of maximum
camber of aft section 112 is between 5 and 12% of the chord.
As shown in FIG. 7, which presents a comparison between thicker
airfoil 30 of FIG. 3a and the airfoil of blade 100 of FIG. 6 (via
an overlay of the airfoil of blade 100 on thicker airfoil 30),
material is removed from pressure surface 104 of the airfoil of
blade 100 relative to thicker airfoil 30. Such material removal
shifts the mean line of the airfoil upward (compare mean line 40 of
thicker airfoil 30 with mean line 114 of the airfoil of blade 100)
and increases the camber (b>a). Mean line 40 of thicker airfoil
30 is confluent with pressure surface 104 of the airfoil of blade
100 along most of its length; therefore, thin aft section 112 is
about half as thick as the aft section of thicker airfoil 30.
Suction surface 36 of thicker airfoil 30 and suction surface 102 of
the airfoil of blade 100 coincide.
A quantitative analysis of the comparison illustrated in FIG. 7 was
performed. For blades with a chord of approximately 75 mm, the
camber at mid-span of thicker airfoil 30 is about 5.7 mm (or 7.7%
of chord) while the camber at mid-span of the airfoil of blade 100
is about 6.7 mm (or 8.9% of chord). Thus, b (=6.7 mm) is about 15%
larger than a (=5.7 mm) in this example.
The "smooth merging" of rounded, thick, bulbous nose section 110
into pressure surface 104 is achieved, for the embodiment of the
invention disclosed, by two blend radii, R1 and R2 (see FIG. 6). R1
forms a convex surface extending from nose section 110 adjacent
leading edge 106 of the airfoil of blade 100 and R2 forms a concave
surface extending from the convex surface to the remaining pressure
surface 104 of the airfoil of blade 100. Large blend radii R1 and
R2 assure that the air flow remains attached over the entire
pressure surface 104. It is very important that the flow remain
attached, to both suction surface 102 and pressure surface 104, to
achieve high lift with low noise and low drag. Preferably, R1 and
R2 are approximately equal and are no less than about 8% of the
chord, c.
For the example airfoil of blade 100 discussed above, having a
chord of about 75 mm, R1 and R2 are both slightly less than 10% of
chord (R1=7.3 mm or 9.7% of chord; R2=7.2 mm or 9.6% of chord).
Rounded, thick, bulbous nose section 110 in that example is about
twice as thick as thin aft section 112.
The design combination of rounded, thick, bulbous nose section 110
(which prevents flow separation); smooth merging of nose section
110 into both suction surface 102 and pressure surface 104 (which
assures that the air flow remains attached over the entire suction
surface 102 and pressure surface 104); and thin aft section 112
(which provides high camber and, consequently, high lift) gives the
airfoil of blade 100 a uniquely efficient profile.
The reduced thickness of the airfoil of blade 100 with respect to
thicker airfoil 30 (FIG. 7) results, of course, in an airfoil with
lower mass. On an experimental blade 100 with the airfoil having
the profile described above, blade mass was reduced by about 35%
relative to a comparable, thicker blade with airfoil 30.
Specifically, blade 100 has a mass of about 19.7 grams while the
blade with thicker airfoil 30 has a mass of about 31.9 grams. The
reduced mass of blade 100 results, in turn, in a fan assembly 10
with lower mass.
As discussed above, the airfoil of blade 100 provides higher camber
and increased lift verses comparable thick airfoil 30. The
high-lift airfoil of blade 100 can be pitched at a lower angle of
attack, therefore, to provide the same lift as thicker airfoil 30.
This is illustrated by FIG. 8, which is a graph of Coefficient of
Lift (C.sub.L) versus Angle of Attack (.alpha.) for an airfoil with
higher and lower camber. The efficiency of the airfoil then
increases as the angle of attack decreases.
Thus, the improvement in lift provided by the airfoil of blade 100
allows reduction in the attack angle. Reduction of the attack angle
permits reduction of the axial depth of ring 14 of fan assembly 10.
This advantage is illustrated in FIGS. 9a and 9b (both figures
depict ring 14 rotating clockwise, when ring 14 is viewed from
above, around its central axis). FIG. 9a shows the axial depth,
x.sub.1, of ring 14 when the airfoil has a high angle of attack.
FIG. 9b shows the axial depth, x.sub.2, of ring 14 when the airfoil
has a lower angle of attack. Clearly, x.sub.2 is less than x.sub.1.
RL is the radius of the ring inlet.
Turning to a specific example, the axial depth of ring 14 when the
airfoil has a pitch of about 15.5.degree. is x.sub.1 =25.4 mm. The
axial depth of ring 14 when the airfoil has a pitch of about
13.5.degree. is x.sub.2 =23.4 mm. Thus, a reduction in axial depth
of x.sub.1 -x.sub.2 =2 mm (or about 8%) is achieved. Ring axial
depth is calculated as RL+Chord.times.sin(airfoil pitch angle). The
radius of the ring inlet, RL, is about 10 mm in this specific
example.
With the airfoil of blade 100 pitched to provide performance equal
to the performance of thick airfoil 30 (i.e., at a decreased angle
of attack), the reduced axial depth of ring 14 resulted in a
decrease of 9% in the mass of ring 14. For the example discussed
above, the mass of ring 14 was reduced by about 7.3 grams (from
about 81 grams to about 74 grams). The lower axial depth of ring 14
results, therefore, in a further reduction in the mass of fan
assembly 10 in addition to the reduced mass of the blades 100. The
total reduction in the mass of fan assembly 10 for the current
example is about 92.7 grams, calculated as the sum of the 7.3 grams
reduction in the ring mass plus an 85.4 grams reduction (12.2
grams.times.7 blades=85.4 grams) in the blade mass.
Consequently, fan assembly 10 has a reduced moment of inertia and
it is easier to balance fan assembly 10. The reduced mass of fan
assembly 10 also contributes to lower vehicle mass and reduces
material costs. Vehicle packaging is also improved because
clearances from fan assembly 10 to adjacent engine components or to
the heat exchanger are increased in the axial direction.
Although it must have a hub 12, fan assembly 10 need not have a
ring 14. The advantageous reduction in the mass of ring 14 provided
by the airfoil of blade 100 would be inapplicable, of course, to
fan assembly 10 without ring 14. Nevertheless, the airfoil of blade
100 would give ringless fan assembly 10 other advantages (such as
packaging) because the airfoil of blade 100 enables a reduced-depth
blade (the blade can be set at a lower angle of attack which allows
the blade to occupy less axial depth).
The outer ends of blades 100 are joined to ring 14 over the full
width of blades 100 and not at a single point or over a narrowing
connecting ring 14. This form of connection is important in
controlling the circulation of the air from pressure (working)
surface 104 to suction surface 102 of blades 100. It also assists
in directing the air onto pressure surface 104 of blades 100 with a
minimum of turbulence. Finally, the support provided by ring 14
provides strength to blades 100.
Ring 14 also improves fan efficiency. Besides adding structural
strength to fan assembly 10 by supporting blades 100 at their tips,
ring 14 holds the air on pressure surface 104 of blades 100 and, in
particular, prevents the air from flowing from pressure surface 104
to suction surface 102 of blades 100 by flowing around the outer
ends of blades 100. Ring 14 preferably has a cross-sectional
configuration that is thin in the radial direction while extending
in the axial direction a distance at least equal to the axial width
of blades 100 at their tips.
A prototype blade 100 using the airfoil described above was built
and tested in a fan assembly 10. Thicker airfoil 30, configured
relative to the airfoil of blade 100 as shown in FIG. 7 (e.g.,
having an identical suction surface), was also tested in a similar
fan assembly 10. Fan assembly 10 included a hub 12 with a diameter
of 130 mm, seven blades (having either the airfoils of blade 100 or
thicker airfoils 30), and a rotating ring 14 with a 340 mm inside
(tip) diameter. The airflow performance test results showed a high
pressure rise with little change in efficiency for the airfoil of
blade 100 as compared to thicker airfoil 30.
The performance information listed below in Table I provides data
for both the airfoil of blade 100 (the light weight or "Lt. Wt."
airfoil) and thicker airfoil 30 (the standard or "Std." airfoil) at
different tip pitch setting angles. The tests were conducted at
room temperature and performance data correspond to an operating
point of 1.4 (non-dimensional)--which represents a vehicle idle
condition.
The operating point of fan assembly 10 is the combination of
airflow through the fan assembly and the pressure rise across the
fan assembly; it is essentially the ratio of pressure to airflow
including additional factors to provide non-dimensionalization.
Higher value operating points indicate higher pressure rise and
lower airflow operation. Lower values indicate higher airflow rates
through, and lower pressure rise across, fan assembly 10.
The non-dimensional operating range for typical automotive
engine-cooling fan assemblies includes values between about 0.7 to
1.5. Idle operation is the most important point for fan assembly
performance. Typical idle operating points range from 1.3 to 1.5.
Thus, this range of fan assembly operation is most important for
performance evaluation of the fan assembly.
The "pumping" performance of fan assembly 10 is defined as the
speed that fan assembly 10 must turn to deliver a given airflow
performance. Pumping, or the flow to speed ratio, changes as a
function of pressure rise and flow operation point of fan assembly
10. It is desirable to have a fan assembly 10 with both high
pumping and high operation efficiency (eta, .eta.). Comparisons of
performance between fan assemblies must be made taking into account
differences in both pumping and efficiency performance.
The "baseline" data point (Note A in Table I) for comparison to the
airfoil of blade 100 is thicker airfoil 30 with a tip pitch setting
angle of 15.5.degree.. Thicker airfoil 30 was also tested at an
18.degree. tip pitch setting angle (Note B in Table I)--although
the airfoil pitch angle twist distribution across the blade span
from tip to hub was unchanged from the baseline design. The setting
angle of the entire blade section was adjusted. This test condition
is included to show the performance of thicker airfoil 30 at a
higher pumping regime.
Fan assembly 10 having blades 100 with the airfoils of the present
invention was tested at a blade tip pitch setting angle (of
15.5.degree.) identical to the baseline test (Note C in Table I).
This test condition shows the impact of the airfoil of blade 100
when compared to thicker airfoil 30. This test condition also
matches the pumping of thicker airfoil 30 at the higher
(18.degree.) pitch angle. Finally, fan assembly 10 having the
airfoil of blades 100 was tested at a blade tip pitch setting angle
of 13.5.degree. (Note D in Table I). This test condition delivers
equivalent airflow performance to thicker airfoil 30 but at a
reduced pitch angle.
TABLE I
__________________________________________________________________________
Fan Assembly Performance Summary for Typical Idle Operating
Conditions Base Equal Airflow Performance Equal Speed Performance
Airfoil Std. Std Lt. Wt. Lt. Wt. Std Lt. Wt. Lt. Wt. Type
__________________________________________________________________________
Pitch 15.5.degree. 18.0.degree. 15.5.degree. 13.5.degree.
18.0.degree. 15.5.degree. 13.5.degree. Degree Note A B C D B C D
Speed 2000 1917 1920 1974 2000 2000 2000 RPM Airflow 24.6 24.6 24.6
24.6 25.7 25.6 24.9 Cmm Eta 46.0% 44.9% 46.0% 47.3% 44.9% 46.0%
47.3% Percent Power 109.8 112.4 109.8 107.6 127.7 124.1 111.4 Watts
__________________________________________________________________________
The data provided above in Table I show that the airfoil of blade
100, tested at the same pitch (15.5.degree.) as thicker airfoil 30,
has the same efficiency (46.0%) and airflow performance (24.6 Cmm)
("Cmm" represents cubic meters per minute) but better pumping (1920
versus 2000 RPM). The pumping of fan assembly 10 with thicker
airfoil 30 at 18.degree. essentially matches (about 1920 RPM) that
with the airfoil of blade 100 at 15.5.degree., but has lower
efficiency (44.9% versus 46.0%). Thus, ring 14 of fan assembly 10
has a lower axial depth with the airfoil of blade 100 than with
thicker airfoil 30 at similar pumping. Finally, the airfoil of
blade 100 at a 13.5.degree. pitch and with a ring 14 of lower axial
depth delivers superior efficiency and pumping performance compared
to thicker airfoil 30 at a 15.5.degree. pitch.
FIG. 10 is a graph of fan assembly static efficiency versus fan
assembly operating point. The typical operating range of 0.7 to 1.5
for automotive cooling fan assemblies is indicated on the graph.
The area of primary interest is in the operating range from 1.3 to
1.5, which represents idle operation. Four curves are provided, one
each for thicker airfoil 30 at a pitch of 15.5.degree., the airfoil
of blade 100 at an equal pitch of 15.5.degree., the airfoil of
blade 100 which matches the pumping of thicker airfoil 30 at a
pitch of 15.5.degree. , and thicker airfoil 30 at a higher pitch of
18.degree.. Inspection of the graph in FIG. 10 shows the improved
efficiency within the idle range of interest for the airfoil of
blade 100 when compared to standard, thicker airfoil 30 with equal
pumping.
In summary, the fan assembly performance test results provided
above evidence increased pumping using the airfoil of the present
invention without significant loss in fan assembly efficiency. The
increased pumping is due to the higher lift provided by the
improved airfoil. A substantially equivalent efficiency performance
combined with increased pumping indicates that lift has increased
in greater proportion to drag. In other words, the airfoil of blade
100 provides a higher lift-to-drag ratio than conventional, thicker
airfoil 30.
Turning to a comparison between the airfoil according to the
present invention and ARMC airfoil 50, FIG. 11 highlights the
difference in profile between the two airfoils. FIG. 11 is an
overlay of ARMC airfoil 50 on the airfoil of blade 100. ARMC
airfoil 50, with its sharp corners 60 and 61 defining straight line
portion 59 on pressure surface 58 (see FIG. 4a), seeks to duplicate
the flow over thicker airfoil 30. In contrast, the airfoil of blade
100 assures attached air flow on pressure surface 104 by a smooth
blend between rounded, thick, bulbous nose section 110 and thin,
highly-cambered aft section 112 (see FIG. 6). Because the airfoil
of blade 100 maintains attached flow in this region of pressure
surface 104, the designer can take advantage of the increased
camber of the airfoil of blade 100, which, as mentioned earlier,
produces increased lift.
Referring to FIG. 4c, first sharp corner 60 bends at an angle
.theta. of at least 30.degree.. In FIG. 12, the airfoil of blade
100 is shown with a first line 116 tangent to nose section 110 on
pressure surface 104 and a second line 118 tangent to the mid-point
of the gradual (not sharp) transition region 120. The resulting
angle, .beta., between tangent lines 116 and 118 is only
24.1.degree.--significantly less than the 30.degree. angle of ARMC
airfoil 50. Although it may vary as a function of chord, camber,
and other characteristics of different airfoils, the angle .beta.
is between 20.degree. and 28.degree..
Discontinuous airfoil 80 with a flat 82 (see FIG. 5) provides
excellent performance across a wide operating range as a blade with
a straight planform. FIG. 13 illustrates a blade with a straight
planform 130. Environmental concerns have prompted, however,
replacement of the chlorinated fluorocarbon-containing refrigerants
(such as R12) used in automotive air conditioning systems with
non-CFC-containing refrigerants (such as R134a). The non-CFC
refrigerants are less effective than the refrigerants they replace
and require increased fan assembly airflow rates to provide
performance equivalent to the CFC-containing refrigerants.
If the existing, straight-bladed fan assemblies were used in the
non-CFC-containing air conditioning systems, the assemblies would
have to operate at higher speeds--thus causing increased airborne
noise. Therefore, a highly-curved blade planform 140 has been used,
as shown in FIG. 14a, to provide the air-moving performance
required by the new air conditioning systems with acceptably low
noise levels. On the new, backward-curved blades used in the air
conditioning systems without CFCs, however, discontinuous airfoil
80 is not as effective as the airfoil of blade 100 with a smooth,
continuous suction surface.
Other aspects of vehicle design, besides the switch to
non-CFC-containing air conditioning systems, have prompted the use
of high-pumping, high-efficiency blades with platform 140. These
aspects include styling (with closed front ends, smaller grilles,
and the like) that increases the system restriction, the need for
increased electrical efficiency which requires more efficient fan
assemblies, reduced packaging space, reduced noise, and reduced
mass. The airfoil of blade 100 with highly-curved blade platform
140 addresses all of these design aspects.
The highly-curved blade planform 140 produces a complex,
three-dimensional flowfield 150 over the blade surface. The
streamlines of such a flowfield 150 are illustrated in FIG. 14b.
The resulting streamlines do not traverse the blade along a
constant radius; rather, the streamlines tend to increase in radius
from the fan inlet to exit. This radial movement of the flow makes
it difficult to design a low-Reynolds-number airfoil such as
discontinuous airfoil 80. The radial shifting of the streamlines,
shown in FIG. 14b, results in an effective airfoil that is quite
different from one designed for a constant-radius airflow.
In contrast, the airfoil of blade 100 of the present invention with
highly-curved blade planform 140 has been successfully tested. The
successful operation of the airfoil of blade 100 on the
backward-curved blade is achieved by the following design features:
a generous leading edge radius (which allows the flow to remain
attached to suction surface 102 over a range of incidence angles)
and high camber (which provides increased lift and pumping). The
sculpted pressure surface 104 maintains the positive performance
achieved by these design features, while at the same time reducing
fan assembly mass and cost. Thus, unlike discontinuous airfoil 80,
the airfoil of blade 100 is suitable for blades with swept or
straight planforms.
In addition to the airfoil discussed above, blade 100 of the
present invention is also provided with a unique, skewed or curved
planform to increase fan performance. The skew refers to the
curvature of leading edge 106 of blade 100 and is illustrated in
FIG. 15. At an arbitrary point 152 on leading edge 106 of blade
100, the skew angle is the angle "T" between a tangent 154 to
leading edge 106 through point 152 and a line 156 from the center
158 of hub 12 (and the center of fan assembly 10) through point
152. The magnitude of skew or planform curvature is defined by the
skew angle, T.
The planform of blade 100 is a composite of three regions having
different planform shapes. The planform is shown in FIG. 16. The
span of blade 100 is defined as R.sub.T -R.sub.H, where R.sub.T is
the tip radius and R.sub.H is the hub radius. For the lower 40% of
the span from hub 12 to ring 14, blade 100 has forward curvature:
leading edge 106 is curved toward the direction of rotation (arrow
160). The platform of blade 100 has little or no curvature (i.e.,
straight curvature) in the interior 20% of the blade span. At the
outermost 40% of the span, blade 100 has backward curvature:
leading edge 106 is curved away from the direction of rotation.
This combination of planform curvature is not arbitrary. The
planform shape was chosen after comparing fan performance data for
three separate blades: one forward-curved, one straight, and one
backward-curved. One important variable in fan design is pressure
rise across the fan (from inlet to outlet plane).
In FIG. 17, normalized total pressure is plotted versus span ratio.
The span ratio is defined as (R-R.sub.H).div.(R.sub.T -R.sub.H),
where r is the local radius. The data show that the most uniform
normalized pressure rise is achieved with a combination of blade
planforms. The forward-curved blade has the highest pressure rise
from the hub to about 40% of span; the straight planform performs
best in the interior 20% of span; and the backward-curved blade has
the greatest pressure rise in the outer 30% to 40% of span-near the
tip of the blade. Because each blade demonstrated superior
performance in a given region of the blade span, blade 100 was
designed with forward curvature in the lower 40% of span, little or
no curvature in the interior 20%, and backward curvature in the
upper 40% of the span. The planform of blade 100 is illustrated in
FIG. 16.
Although the dimensions of blade 100 incorporated in fan assembly
10 will vary depending upon the application of fan assembly 10, the
dimensions discussed above describe a preferred form of the
invention suitable for use in a number of automotive
applications.
A blade with planform curvature produces lower airborne noise than
a blade with a straight planform. Even with the optimized pressure
loading of blade 100 described above, however, there is still a
drop in net airmoving performance associated with the curved
planform blade. This performance loss is the result of the downwash
that exists on any swept wing or blade. Downwash is the term used
to describe the upstream tangential velocity component that is
induced by trailing-edge vortices. This induced tangential velocity
reduces the airfoil's effective angle of attack and, consequently,
reduces lift and blade pumping.
Typical inlet velocity diagrams for an airfoil of a blade with a
straight planform and for an airfoil of a blade with a curved
planform are shown in FIGS. 18a and 18b, respectively. In each
case, "P" is the pitch angle of the blade. The linear blade speed
is represented by .omega.r, where .omega. is the angular speed of
the blade and r is the radius. In an axial flow fan assembly 10,
the air flow has components of velocity parallel to the axis of
rotation of fan assembly 10 (v.sub.a) and to the tangential
direction (v.sub.T)--but has little radial velocity. The angle of
attack (.alpha.) for air stream 18 is represented by .alpha..sub.s
for the straight planform blade (FIG. 18a) and by .alpha..sub.c for
the curved planform blade (FIG. 18b). Note that .alpha..sub.c
<.alpha..sub.s.
Several alternatives exist for recovering the airfoil performance
lost to downwash on curved planform blades. One solution is to
operate the fan assembly having curved planform blades at a higher
speed to match the airflow of the straight planform blades. This
alternative is undesirable because the noise increases at the
higher speed. Another option is to increase the pitch angles of the
airfoils, which will increase pumping and deliver the required flow
without an increase in speed. Although this option will not
increase the fan noise, a deeper fan package is required because
the fan depth is a function of airfoil pitch expressed by:
where D(r) is the blade depth at radius r, C(r) is the airfoil
chord, and P(r) is the airfoil pitch angle as shown in FIGS. 18a
and 18b. With the restriction in available underhood space in
modern automobiles, it is important to keep the depth D as small as
possible.
Another alternative is to increase the chord length C. This
alternative will increase the lift of the airfoil and the pumping
that the blade can produce. An increase in chord C(r) produces an
increase in depth D(r), however, as given in equation (1)
above.
A fourth approach is to modify the design of the airfoil itself to
create more lift (and, thereby, more pumping) without increasing
the airfoil pitch angle or chord. As mentioned above, airfoil lift
increases with increased camber. To produce equivalent lift with a
cambered airfoil, the pitch angle of the airfoil can be reduced.
This is shown in FIG. 8, which is a graph of Coefficient of Lift
(C.sub.L) versus Angle of Attack (.alpha.) for an airfoil with
higher and lower camber.
Pressure surface 104 of blade 100 combining the high-lift airfoil
and curved planform is illustrated in FIG. 19. By providing a blade
100 with the high-lift airfoil having a bulbous leading edge (see
FIG. 6) and with the 40% forward curvature, 20% straight, 40%
backward curvature planform from hub 12 to ring 14 (see FIG. 16),
reduced noise and proper loading of blades 100 are achieved. Fan
assembly 10 having blades 100 also has a good operating efficiency.
These operational improvements are achieved through a combination
of both the high-lift airfoil and curved planform features of blade
100.
Test results validate the improvement in operation. Three types of
prototype blades were built and tested in fan assembly 10 for
comparison. The first blade (Blade 1) has a straight planform and
the conventional thicker airfoil 30 shown in FIG. 3a. Blade 1
provides a baseline. The second blade (Blade 2) has the same
airfoil as Blade 1, but has the 40%-20%-40% curved planform
described above and shown in FIG. 16. The third blade (Blade 3) has
both the high-lift airfoil with a bulbous leading edge, as
described above and shown in FIG. 6, and the 40%-20%-40% curved
planform. Equal airflow performance was chosen as the basis for
comparison: fan speed was adjusted to match the volume flow rate of
the Blade 1 fan at 15.degree. tip pitch angle at a speed of 1850
RPM. Results are shown in Table II below:
TABLE II ______________________________________ Equal-Airflow
Comparison Blade 1 Blade 2 Blade 3 (straight (curved (curved
planform; planform; planform; standard airfoil) standard airfoil)
high-lift airfoil) ______________________________________ Eff, %
45.4 48.0 46.9 Speed, RPM 1850 1954 1914 Noise, dB (A) 75.6 72.9
72.2 baseline same pitch same pitch performance as Blade 1 as Blade
1 ______________________________________
Test results show that blade planform curvature alone results in a
2.7 dB(A) noise reduction, but requires an additional 104 RPM to
match the baseline airflow performance (Blade 1 versus Blade
2).
To recover lost airflow while maintaining the noise reduction of
the curved planform blade, Blade 3 was built with both planform
curvature and the high-lift, bulbous-leading-edge- airfoil. Blade 3
required a speed of 1914 RPM to match baseline performance and
provided a noise level of 72.7 dB(A). For Blade 3 to match the
baseline airflow at a speed of 1850 RPM, the pitch angle must me
increased from 15.degree. to 17.5.degree.. For Blade 2 to match
baseline airflow at 1850 RPM, the pitch angle must be increased
from 15.degree. to 19.degree..
Note that even at the higher fan speeds required for Blades 2 and 3
to match the baseline (straight planform) airflow of Blade 1, the
noise generated by these curved planform blades is lower. In the
case of Blade 2 (curved planform, standard airfoil), the noise is
2.7 dB(A) lower than Blade 1; Blade 3 is 3.4 dB(A) quieter than
Blade 1 at the equal-airflow operating speed.
The advantage of using the high-lift airfoil is shown by comparing
Blade 2 with Blade 3. To match the straight planform blade airflow
at 1850 RPM, Blade 2 standard airfoil) required an increase in
pitch angle of 4.degree.. Blade 3, with the highly-cambered
high-lift airfoil, required an increase in pitch angle of only
2.5.degree.. The 1.5.degree. of decreased blade pitch (Blade 3
versus Blade 2), on a blade with a tip chord of 56.0 mm, would
result in a 5% decrease in ring axial depth. This corresponds to a
mass decrease of 5.0 g (assuming a 1.4 mm decrease in ring depth,
thickness of 2.5 mm, ring radius of 161.25 mm, and the density of
Nylon 6/6 of 1.42 grams per cubic centimeter).
The decrease in the axial depth of ring 14 may be leveraged in one
of two ways: fan assemble 10 could be pulled forward, away from the
engine, thus increasing clearance between fan assembly 10 and
underhood components; or, fan assembly 10 could be pulled rearward,
away from the heat-exchanger face, thus improving the ability of
shrouded fan assembly 10 to draw air from the corners of the heat
exchanger. In either case, the decreased axial depth of fan
assembly 10 works to the advantage of the engine-cooling system
designer. The extremely tight packaging in the underhood of modern
vehicles makes even this small improvement in the axial depth of
fan assembly very important.
Moreover, the mass of Blade 3 (curved planform, high-lift airfoil)
is 9.3 g less than the mass of Blade 2 (curved planform, standard
airfoil). This is a 34% reduction in blade mass compared with the
conventional thick-airfoil blade.
Blade 100 can have either of the two, separate characteristics
(curved planform and high-lift airfoil) discussed above.
Preferably, however, blade 100 has both characteristics. Blade 100
with the combination of three planform shapes discussed above
produces low airborne noise with a uniform spanwise pressure
loading. To compensate for the reduced pumping that is a
consequence of curving the blade planform, a special high-lift
airfoil is used. The combination of the curved planform and
high-lift airfoil gives fan assembly 10 the required airmoving
performance.
Blade 100 with a curved planform and high-lift airfoil results in a
near-uniform span-wise pressure loading with high efficiency, low
airborne noise, and low mass. The unique airfoil operates at a
lower angle of attack than a conventional thick airfoil, which
results in less ring and blade axial depth and an associated
decrease in axial packaging space. The reduction in fan and ring
axial depth (compared with a curved blade with conventional thick
airfoils) allows for easier packaging and better airflow through
the heat exchanger.
Although illustrated and described herein with reference to certain
specific embodiments, the present invention is nevertheless not
intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims and without departing from the spirit
of the invention. The engine-cooling fan assembly in which the
airfoil of the present invention is incorporated, for example, may
be powered by a fan clutch, an electric motor, or an hydraulic
motor and may be used with or without an attached rotating
ring.
* * * * *